Manganese-Catalyzed Oxidation with Hydrogen Peroxide

Mariganese-containing catalases have been isolated from three species of bacteria Lactobacillus plantarum [27], Thermus ihemtophUus [28], and Thermoleophilum album [18]. X-ray crystallographic structure analysis [29] has shown that these catalases contain a dinudear manganese core. During catalysis, the dinudear manganese active site cydes between the Mn - and Mn2 oxidation states [30]. 

EPR [31], NMR[32], and UV-Vis [32a] spectroscopic studies have identified that in the disproportionation of H2O2 both Mnj and Mnj oxidation states are involved [33]. 

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Manganese-Catalyzed Oxidation with Hydrogen Peroxide... 

CA[Mn] efficiently catalyzed the oxidation of o-dianisidine to the red quinonedi-imine with hydrogen peroxide (Scheme 2). This o-dianisidine oxidation is a common assay for peroxidase [47-50] or for peroxidase-based detection of hydrogen peroxide [51]. As control reactions, native zinc carbonic anhydrase showed <1% of the activity of CA[Mn], while the same concentrations of manganese(ll) chloride and bicarbonate alone showed only 5% of the activity of CA[Mn]. Unlike other peroxidases [47-50], the CA[Mn]-catalyzed oxidation of o-dianisidine required bicarbonate and showed only 1.5% of the activity in the absence of bicarbonate. 

Several chemocatalytic systems for sulfoxidation that employ other oxidants than hydrogen peroxide, molecular oxygen, or alkyl hydroperoxide have been reported. Manganese-catalyzed oxidation of sulfides with iodosobenzene (PhIO) using chiral Mn(salen) complexes was used to obtain chiral sulfoxides in up to 94% ee [71]. PhIO was also employed as the oxidant in sulfoxidations catalyzed by quaternary ammonium salts [72]. The use of cetyltrimethylammonium bromide (n-Ci6H33Me3N Br ) gave the best result, and with 5-10 mol% of this catalyst, high yields (90-100%) of sulfoxide were obtained from various sulfides. 

Lignin (LiP) and manganese dependent (MnP) peroxidases of R chrysosporium are secreted in conjunction with a number of other enzymes and chemicals under nutrient deficient conditions (3, 33, 44-47, 86, 92, 93). The peroxidases are known to catalyze a number of free radical reactions. Research on these enzymes has been extensively reviewed recently (5, 49, 85). The resting enzyme (ferric-heme protein) is initially oxidized by two electrons in a reaction with hydrogen peroxide (Fig. 6). The resulting intermediate, com-... 

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